The invention relates generally to an improved apparatus and method for excising atheromas from the lumina of blood vessels and diseased tissue from other interstitial body spaces. More particularly, the invention relates to new and improved catheter-borne atherectomy systems for removing diseased tissue from the lumina of human arteries and which can be adapted to ablate glandular tissue, for instance, in a prostectomy.
Fatty deposits accumulated in the coronary or peripheral arteries of a human patient are known to threaten health. Once such a condition has been diagnosed, a physician has available several different courses of treatment. One of these is bypass surgery, in which a portion of the affected vessel is replaced with a portion of a healthier vessel. This method typically is viewed as a last resort because it involves open surgery which inherently presents more risk to a patient than other available methods.
Another treatment method is angioplasty, in which a balloon catheter is inserted into the body and the balloon is positioned where the disease occurs, referred to variously as the stenosis, atheroma, and plaque. The balloon then is inflated under pressure to press the stenosis against the walls of the vessel in order to expand the lumen and thereby increase blood flow.
An atherectomy is a third method for treating stenosed portions of an artery or other vessel. This procedure involves the resection of the atheroma from the affected vessel with a cutting device which is carried to the location at which treatment is to be rendered by a catheter.
Prior art atherectomy catheter systems include a generally circular cylindrical housing bearing a cutting blade, the housing being mounted on a balloon catheter. The cutting surface of the blade has a curvature which approximates the curvature of the housing. The housing has a cutout or window near its distal end, and a guidewire is used to position the catheter and the housing window at the affected site in the blood vessel. The balloon is inflated to push the window up against the plaque and the cutting blade is pushed into the window. The blade slices off the atheroma as it slowly traverses the length of the window, and the cut material falls into the window. Some of these atherectomy systems include an element to push the cut material into the nose of the housing and to retain it there until after the catheter system is removed from the patient, to prevent the tissue debris from entering the blood stream and possibly causing complications.
In such systems, the cutting blade commonly is cylindrically-shaped, such that the curvature of the blade roughly approximates but may not match the curvature of the arterial wall, because the curvature of the wall most often is ellipsoidal. Thus, it can be difficult to cut all of the material targeted for resection on a single pass of the blade. The efficiency with which the procedure can be accomplished is adversely impacted by the need to resort to multiple passes of the blade and the attendant need to proceed more slowly as deeper and deeper cuts are made to avoid resecting healthy tissue along with the plaque. Further, care must be taken when performing an atherectomy with a system incorporating a blade that cuts as it advances along the longitudinal axis of the artery, as this type of cutting action can have a tendency to cut more and more deeply into the luminal surface as the blade advances. This can result in an uneven luminal surface which might lead to less than optimum blood flow or might increase the likelihood that stenosis will reoccur at the site treated by the atherectomy. When such prior art atherectomy systems are used to perform prostatectomies, the need for precision also can make it time-consuming to avoid inadvertently cutting or burning non-prostatic tissue surrounding the prostate gland.
Atherectomy systems also can be adapted for use in prostatectomies in which an enlarged or diseased prostate gland is removed. In such a procedure, the atherectomy system is enhanced with a heating element and is used in transurethral resection of the prostate, the catheter usually being inserted through a channel of a cystoscope to deliver the excising or ablating element and associated heating element, which are used to accomplish the resection by a combination of cutting action and of selectively increasing the temperature of the excising or ablating element to facilitate ablation of the glandular tissue. As is the case in the atherectomy application, catheter-borne systems can lead to inefficiency when used in prostatectomies, due to the time-consuming attention to precision that is mandated because of the shape and cutting path of the blades. Care must be exercised so that only the target tissue is ablated.
What has been needed then, and what has heretofore been unavailable, is a system that can deliver a cutting mechanism to a vessel or organ designated for treatment via a device such as a catheter, which avoids resort to open surgery, and that is configured to allow precise cutting action without compromising the overall efficiency with which the procedure can be accomplished.